Celestine: Celestine appears as colorless, or pale blue, and is transparent to translucent, and has two directions of cleavage. It is very brittle, and has a vitreous to pearly luster. It occurs in sediments associated with sulfur, with evaporate minerals like gypsum, anhydrite, and halite; in hydrothermal veins with galena and sphalerite; as concretions in clay and marl; in cavities in basic lavas, and i (read full)

Gypsum: Gypsum is the most common sulphate mineral. It is usually the first evaporite mineral to be precipitated form water due to its poor solubility. Varieties include Selenite (or "spectacle stone), which is colorless and transparent; Satin Spar, the fibrous, translucent form with silky luster, which when cut cabochon shows pearly chatoyant effects; Alabaster, used for ornaments, which is firm, fine-gr (read full)

Petalite: Petalite is a lithium aluminum silicate that is an important ore of lithium. This mineral forms, rarely, as small crystals, which are commonly twinned. More often, petalite forms as large, cleavable masses. It may be white, grey, pinkish, yellow, or colorless. It is transparent to translucent, with a vitreous to pearly luster, and fuses with difficulty. It forms in very coarse-grained, acid igne (read full)

Calcite: Of all minerals, calcite is by far the richest in forms. It appears as rhombohedral, scalenohedral, or prismatic crystals, often intergrown or twinned. It occurs in masses, colorless or in white, pink, green, or yellow, and often visibly thermoluminescent (emits light when heated). Like quartz, calcite often has twinned structure caused by temperature and stress changes. It is semi-hard, wit (read full)

Dolomite: Dolomite is similar to calcite and sits along side it in limestone. It usually occurs as a secondary mineral, formed by the reaction of magnesium-bearing fluids seeping through the limestone. It may be colorless, or white to cream and even yellow brown, sometimes pale pink. It has a vitreous luster and is translucent. The faces of dolomite crystals are often curved, sometimes so acutely that th (read full)

Kyanite: Kyanite is an aluminum silicate that occurs as elongated and tabular in groups of light-blue crystals darker toward the center, or flat, bladed crystals in schists and gneisses, or as radiating rosettes in quartz. It is trimorphous with sillimanite and andalusite. Kyanite is also known as disthene, meaning, "double strength." This refers to the fact that the hardness along the length of kyanite c (read full)

Sillimanite: Sillimanite is a grayish-blue aluminum silicate with an orthorhombic crystal system. It is trimorphic with andalusite and kyanite. All three have the same chemical compound but their atoms each arrange to create three different crystal forms. It appears as long, slender crystals without distinct terminations, in off-white, gray, brown, pale green, slate-blue, blue-green, and these crystals are of (read full)

Enstatite: Enstatite is the most common silicate under the Orthopyroxene group in the larger classification of Pyroxene minerals (which are rock-forming silicates). Orthopyroxenes form a chemical series composed of the magnesium-rich enstatite, and the iron-containing bronzite and hypersthene. It has an orthorhombic crystal system and appears rarely as stubby, prismatic crystals, but more commonly in fibr (read full)